The present invention relates to a liquid crystal display device (LCD). More particularly the present invention relates to a LCD driven by electrically connecting a tape automated bonding integrated circuit (TAB IC) with a printed circuit board (PCB).
In conventional integrated circuits, electric wires are generally connected by soldering, a method involving connecting solid metals using a medium such as a solder through a thermal process. A soldering method joins solid metal pieces together using a solder that has a lower melting point than those of solid metals to be connected. The solder is melted and diffused during the melting process by a capillary action to connect two or more solid metal pieces into a single assembly.
A conventional LCD module manufacturing process includes a TAB-solder step for thermally compressing a solder-coated pad on a TAB IC after an out leader bonding (OLB) process. In the TAB-solder step, the solder-coated pad on the PCB and a solder-coated lead of a TAB IC are connected by thermal compression. During thermal compression, a solder cream is melted from the solder-coated pad on the PCB to cover the solder-coated lead of the TAB IC, thus connecting the solder-coated pad on the PCB to the solder-coated lead of the TAB IC. Because of the importance of this connection, the solder-coated pad on the PCB should be carefully matched to the solder-coated lead of the TAB IC during the thermal compression step. In addition, it is important to have a structure that can help the diffusion of the solder cream in this method.
FIG. 1 is a diagram showing a connection state among a liquid crystal panel, the TAB IC and the PCB in a conventional LCD, and FIG. 2 is a side view of the device in FIG. 1.
As shown in FIGS. 1 and 2, the TAB IC 13 electrically together with peripheral circuits (not shown) on a PCB 15 drives a liquid crystal panel 11. The TAB IC 13 serves to electrically connect the PCB 15 and the liquid crystal panel 11.
FIG. 3 is a perspective view of a solder-coated pad 33 on a PCB and a solder-coated lead 31 of a TAB IC 13 in a conventional LCD. The solder-coated lead 31 of the TAB IC and solder-coated pad 33 on the PCB shown in FIG. 3 are both comprised of lead and both have a rectangular shape. In this structure, a horizontal side length L.sub.1 of the solder-coated lead 31 of the TAB IC is the same as a horizontal side length L.sub.2 of the solder-coated pad 33 on the PCB.
FIG. 4 is a diagram showing a state where the solder-coated pad 33 on the PCB and the solder-coated lead 31 of the TAB IC, shown in FIG. 3, are soldered together. As shown in FIG. 4, during the process of thermally soldering them, the solder cream is diffused from the solder-coated pad on the PCB into the solder-coated lead of the TAB IC. When using the solder-coated pad 33 and the solder-coated lead 31 of FIG. 3, the diffusion of solder from the solder-coated pad 33 onto the solder-coated lead 31 occurs in a pattern similar to that shown by the shaded portion 41 in FIG. 4. Here, the solder cream is only partially diffused into the solder-coated lead of the TAB IC, resulting in a lower soldering quality of the contact between the solder-coated lead of the TAB IC and the solder-coated pad on the PCB. Because of this lower quality soldering, the two components are occasionally electrically isolated.
Much of the shape of the diffusion of solder results from the shape of the solder-coated lead 31 and the solder-coated pad 33 and the fact that the horizontal side length L.sub.1 of the solder-coated lead 31 of the TAB IC is the same as the horizontal side length L.sub.2 of the solder-coated pad 33 on the PCB. In order to increase the quality of soldering between the solder-coated lead 31 of the TAB IC and the solder-coated pad 33 on the PCB, it is desirable that their shapes should be different to widely diffuse the solder cream during the soldering process.